This invention relates to a method of fabricating a drive shaft to accommodate axial movement between a vehicle transmission and a drive axle.
Typically, a driveline for a motor vehicle includes a shaft extending along an axis between a transmission and a differential of a drive axle. Each end of the shaft includes a yoke that forms one portion of a U-joint. The U-joint allows movement of the shaft member to accommodate movement of the drive axle due to road imperfections.
One type of shaft or driveline is designed to further accommodate movement of the drive axle. Typically, such a driveline includes mated first and second mated members slidably disposed relative to each other along a common axis. The first and second members are fabricated from thin walled tubes to form inner and outer interlocking profiles engaged to one another to transmit torque and accommodate axial movement. Clearance between the interlocking profiles is critical to operation of the driveline assembly. Excessive clearance will cause excessive noise and inefficient torque transfer and insufficient clearance prevents the required axial movement between driveline members. A consistent clearance between the first and second interlocking profiles is accomplished in one type of driveline assembly by injecting an elastomeric material between the interlocking profiles at an elevated temperature and then cooling the elastomeric material. The subsequent thermal contraction of the elastomeric material provides the predetermined clearance between the interlocking profiles.
The injection of the elastomeric material is somewhat complex especially for tubes of longer lengths; therefore, it is desirable to develop a method of forming a predetermined clearance between inner and outer interlocking profiles that does not require the use of an elastomeric material.
An embodiment of this invention is a method of fabricating a driveline assembly including first and second members with interlocking torque transferring profiles formed concurrently to provide a predetermined clearance such that the first and second members are axially movable relative to each other.
The method of this invention includes the steps of inserting a first hollow member within a second hollow member, and placing both members into a die. The die includes an inner surface with an interfitting torque transmitting profile. Pressure applied to an inner diameter of the first member causes the first member to expand into the second member and in turn into the profiled inner surface of the die.
The temperature of the first member is elevated relative to the second member such that the first member has thermally expanded an amount greater than thermal expansion of the second member. With the temperature of the first member elevated above that of the second member the pressure applied to the first member drives the first member outwardly into the second member and further into the inner surface of the die. A pressurized fluid applies pressure to the first member by filling the inner diameter of the first member.
The fluid is then removed and the first and second members removed from the die. Because the first member was at an elevated temperature and had thermally expanded a greater percentage relative to that of the second member, the first member will shrink or contract a greater amount than that of the second member. The difference in the amount that the first member contracts relative to the second member provides the predetermined clearance between the interlocking profiles.
In another embodiment of this method, the interlocking profiles of on the first and second members are formed by way of a die and mandrel. In this embodiment a first tube is placed within a second tube and both placed within a die. The inner surface of the die is in contact with the outer member and includes a shape to form the interlocking profiles. A mandrel including an outer surface shaped to form a mating profile to that of the die is pushed into the first member. Forcing the mandrel into the first member forces the two members to take the shape formed between the die and the mandrel.
Interlocking profiles can be formed along substantially the entire length of the two members are in discrete locations depending on the desired configuration of the driveline.
The method of this invention provides a simple, low cost and reliable method of forming a predetermined and uniform clearance between interlocking profiles such that the members of the driveline are free to move relative to each other along the common axis.